1. Field of the Invention
The present invention relates generally to a fast handover method. More specifically, the present invention relates to a fast handover method optimized for the Institute of Electrical and Electronics Engineers (IEEE) 802.11 networks which support a node being fast handed over through a pre-operation for the fast handover.
2. Description of the Related Art
Recently, with the rapidly increasing use of the Internet, the development of radio communication technology, and the improvement of performance of mobile terminals such as portable computers and personal digital assistants (PDAs), a great number of users use wireless Internet. Under a wireless Internet environment, the mobile terminal occasionally changes a network attachment point due to a movement of a location of the mobile terminal.
In order for the mobile terminal to perform wireless Internet communications, even when the mobile terminal moves into a foreign network out of its home network, a similarly high quality Internet service as that of the home network should be assured. As for the mobile terminal changing a network attachment point, a variety of technologies have been proposed to provide stable wireless Internet services. In particular, the mobile IP working group of the Internet Engineering Task Force (IETF) has proposed a method by which all mobile terminals may continuously use a specific identifier, referred to as an IP address, regardless of the network attachment point. The mobile IP working group defines a mobile IP protocol and tries to complement defects. Also, in order to overcome a problem in which the existing IPv4 address system cannot accept increasing demand for more addresses, the introduction of mobile IPv6 technology is underway to provide wireless Internet service using the IPv6. Since the mobile IPv6 has been introduced, this system has been revised to become IETF Internet-draft version 24 and plans are underway for the system to become a Request For Comments (RFC) system.
In accordance with the mobile IPv6 technology, even when a mobile terminal moves into a foreign network, the mobile terminal remains in communication with a correspondent node (CN) using a home address (HA) thereof via a home agent (HA). The HA is a router having registration information of the mobile terminal. When the mobile terminal is linked to the foreign network, the mobile terminal is assigned a care-of Address (CoA), which is a temporary address, from an access router of the foreign network, and registers the assigned CoA along with the home address at the home agent, which is called a binding.
Accordingly, the home agent intercepts packets from the correspondent node to the mobile terminal, and forwards the intercepted packets to the mobile terminal located at the foreign network using a current CoA of the mobile terminal.
In order to be assigned a CoA, the mobile terminal establishes a link layer connection to the foreign network, and then receives a router advertisement (RA) message from a router of the foreign network. To this end, the mobile terminal may multicast a router solicitation message to the entire network.
The router advertisement message provides prefix information of the network. Accordingly, the mobile terminal generates a new CoA using the prefix information of the network and a link-layer address (LLA) thereof. The mobile terminal sets the generated CoA to the temporary address thereof.
When determining whether the CoA is generated according to the movement of the mobile terminal to another network or the re-set of the network interface of the mobile terminal is impossible, a delay should be carried out over a time between 0 and 1 second.
Next, the mobile terminal multicasts a neighbor solicitation message including its LLA to the newly linked network, and commences a duplicate address detection (hereinafter, to be referred to as DAD).
If the neighbor advertisement informing that the duplicate address is not received at the mobile terminal within a predetermined time limit (RetransTimer), the corresponding CoA is regarded as a unique CoA and the mobile terminal performs communications using this unique CoA over the network. The predetermined time limit is 1000 ms by default.
According to the mobile IPv6 standard, when the mobile terminal gets a new link, that is, when the mobile terminal moves into a new IP subnet, a fast handover in mobile IPv6 (FMIPv6) has been proposed as a protocol to minimize handoff latency and packet loss, which is planned to become an RFC in time.
However, the FMIPv6, which uses a lot of handover-related signalings, has considerable problems. In particular, the FMIPv6 is in the standardization process without being optimized for the IEEE 802.1x network. The following explains the problems of the conventional fast IPv6 handover method.
First, that the conventional fast IPv6 handover is carried out in a preactive mode based on movement prediction is assumed. However, it is not clearly specified when the mobile terminal goes through layer 2 handover when the movement prediction is successful at the link before the movement. Thus, packet loss may happen when the layer 2 handover is not correctly performed after a packet tunneling request message is sent to the layer 3.
The movement prediction is divided roughly into movement detection, and new CoA configuration and confirmation. As the conventional fast IPv6 handover carries out the two processes separately, a pre-operation for the handover requires quite a long time and chance of the successful handover based on the prediction lowers.
For the mobile terminal to check the address duplication when generating a temporary address thereof to be used at the new link takes approximately 1000 ms. Such a required time raises the most serious problem to the fast handover.